During the process of soldering when surface mounting electronic components on a printed wiring board by protecting the wiring (circuit) pattern formed by a method such as screen printing on the board from the external environment, in order to protect the printed wiring board so that solder is not adhered to those portions where it is not required, a protective layer referred to as a cover coat or solder mask is covered over the printed wiring board.
Although primarily multifunctional epoxy resin-based compounds were used in the past for the solder resists used in such applications, although the resulting cured film has satisfactory heat resistance, it had the problem of low flexibility (see Patent Document 1 below). Thus, the applications of this solder resist were limited to rigid boards not requiring flexibility (bendability) of the cured film, and this solder resist had difficulty in being used for flexible printed circuit (wiring) boards (FPC) which have come to be used frequently in recent years.
In consideration of these circumstances, numerous solder resists having flexibility have been proposed in recent years, and the present applicant, for example, proposed the use of a composition containing a urethane (meth)acrylate compound having a carboxyl group as a coating material of FPC boards and other printed wiring boards (see Patent Document 2 below).
Although this composition has superior flexibility and can be adequately applied to FPC boards, further improvement of performance is sought with respect to electroless gold plating resistance.
[Patent Document 1] Japanese Unexamined Patent Publication No. 11-228688
[Patent Document 2] Japanese Unexamined Patent Publication No. 2002-229201